This invention relates generally to drilling machines and more particularly to systems for raising and lowering drilling heads on drilling machines. Drilling machines used in applications such as blast hole, water well, shallow oil and gas exploration, require the use of long straight sections of drill pipe which are connected to the rotary drilling device, (rotary head), to perform the drilling process. Most drilled holes are deep enough to require additional drill pipe to be added to the drill string to complete the hole. Subsequently, each added drill pipe must be removed from the drill string before the drilling machine can be moved to the next hole location.
It is advantageous to reduce time intensive procedures from the drilling process that are not actually performing the drilling of the hole. One trend is to lengthen each section of drill pipe which reduces the number of sections to be added and eventually subtracted from the drill string. Logically, increasing the feed speeds up and down would also reduce the trip time for each drilled hole.
There are basically two types of systems that control the up and down rectilinear motion and feed forces of the rotary head. They are cylinder feed and motor feed.
Motor feed systems are very expensive compared to the cylinder feed systems. This is mainly due to the fact that roller chains must be used. These chains are extremely heavy. Handling the extra weight requires a robust tower which adds cost. Drive motors, fail-safe brakes, and speed reducing planetary gear boxes are other essential and expensive items which are characteristic of motor feed systems.
A motor feed system is normally used when the rotary head travel becomes so long that it is impractical to use a cylinder for feed control. This is because the piston rod diameter must be sized larger to prevent buckling. At the same time, it forces the bore diameter of the cylinder to grow so the pulldown and pullback force requirements can be maintained. Consequently, the feed speeds slow down because the volumes on both sides of the piston have increased. To combat the slow speeds, larger and more expensive pumps must then be selected. Also, the hydraulic system as a whole must be more expensive to handle the larger flow required.
The foregoing illustrates limitations known to exist in present feed systems for drilling machines. Thus it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly a suitable alternative is provided including features more fully disclosed hereinafter. The system described here allows the use of a cylinder feed system for drill rod lengths that, in the past, would have required the use of an expensive motor feed system.